The present invention concerns a patient positioning system for radiotherapy, or for radiation therapy or radiosurgery. In principle, the procedure within the framework of such radiation treatments is that radiation planning is undertaken first of all, wherein image recordings are taken of the patient or of the area of the patient around the radiation target, for example computer tomography recordings. The treatment target is registered via known marking systems. In accordance with the present standard, the patient is then taken off the bed at the image-generating device, and goes independently to the radiotherapy room in order to lie down there on another bed at the radiotherapy apparatus. Here, one attempts via a tracking system to determine the current position of the radiation target, using the position of the markings arranged on the patient, and/or to position the patient by means of a tracking system, such that the treatment target lies in the isocenter of the radiotherapy apparatus. Typically, the image data for planning are not recorded on the same day as treatment takes place.
This approach involves a great disadvantage, alone because of the movement of the patient between the two patient beds. Markings which are mostly arranged on the patient's skin shift during this relocation, in relation to each other and to the radiation target point. Positioning for radiation exposure on the radiotherapy apparatus, and therefore the radiotherapy itself, thus becomes imprecise, which possibly brings the success of the treatment at least partly into question.
A similar problem arises if the position of the radiation target is dependent on the respective breathing state of the patient. If the patient's planning data set, for example, was recorded while the patient was holding his breath, this data set represents the patient and the position of the target volume at a specific lung filling. In order to be able to transfer these data to the state of the patient at the time of radiation exposure, the lung filling would have to exactly correspond at the two points in time. If the patient is able to breathe freely during radiation exposure, this is at most the case at two points in time per breath. Moreover, the breathing drift, being a shift of the underlying lung volume over medium periods of time, will present a problem.
Here too, the problem arises of the transferability of the 3D planning data set to the state of the patient at the time of radiation exposure.
Previous approaches for solving the above latter-mentioned problem have made use of the fact that a patient's breathing may be tracked by observing the outer contour of the thorax and abdomen. If markings are arranged on the patient's skin, these can then be correlated with the position of inner target volumes. However, if the patient is relocated after the image-generating examination (for example CT, MR, SPECT, PET) has been carried out—wherein the patient typically has to get up, walk to the radiotherapy room, and there lie down on another bed—then the sebaceous layers of the patient again slip here, and therefore also the markings arranged on them. This in turn results on the one hand in an inaccurate position of the patient co-ordinate system, as well as to a clear distortion of a possibly previously determined correlation between the breath-dependent position of the target volume and the external markings. For this reason, in accordance with a known approach to solving this problem, correlation is carried out directly, on the radiotherapy apparatus table. This in turn is disadvantageous, because the image-generating methods usable are either of a lower quality compared to the devices described above, or require a high level of investment, since either the therapy device or the image-generating device may be used, but not both at the same time.